When we write RecyclerView as GridView style, and write RecyclerView item as focusable and there is a focus frame, when we scroll RecyclerView with focus, we will find that there is a bug in the focus jump of RecyclerView, which is inconsistent with the focus jump rules we want. The bug that appears is as follows:
The black box represents the screen. When we press the focus from an item in the upper left corner, when we need to load a new line, the focus goes to the last item of the new line. (As shown in the figure, item1 was originally obtained. Focused, the result ran to item2).
This is a bug of RecyclerView. I remember that when RecyclerView first came out, the scrolling was still a little stuck. Now it is still very smooth to scroll. It takes time to settle a new artistic space. We can recreate this bug. Write GridLayoutManger to solve. Look directly at the code:
package com.wasu.cs.widget;
import android.content.Context;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.view.View;
/**
* Customize GridLayoutManager, modify the BUG of RecyelerView focus jumping
* Created by Danxingxi on 2016/4/1.
*/
public class FocusGridLayoutManager extends GridLayoutManager {
/**
* Constructor used when layout manager is set in XML by RecyclerView attribute
* "layoutManager". If spanCount is not specified in the XML, it defaults to a
* single column.
*
* @param context
* @param attrs
* @param defStyleAttr
* @param defStyleRes
* @attr ref android.support.v7.recyclerview.R.styleable#RecyclerView_spanCount
*/
public FocusGridLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}
/**
* Creates a vertical GridLayoutManager
*
* @param context Current context, will be used to access resources.
* @param spanCount The number of columns in the grid
*/
public FocusGridLayoutManager(Context context, int spanCount) {
super(context, spanCount);
}
/**
* @param context Current context, will be used to access resources.
* @param spanCount The number of columns or rows in the grid
* @param orientation Layout orientation. Should be {@link #HORIZONTAL} or {@link
* #VERTICAL}.
* @param reverseLayout When set to true, layouts from end to start.
*/
public FocusGridLayoutManager(Context context, int spanCount, int orientation, boolean reverseLayout) {
super(context, spanCount, orientation, reverseLayout);
}
/**
* Return the current number of child views attached to the parent RecyclerView.
* This does not include child views that were temporarily detached and/or scrapped.
*
* @return Number of attached children
*/
@Override
public int getChildCount() {
return super.getChildCount();
}
/**
* Return the child view at the given index
*
* @param index Index of child to return
* @return Child view at index
*/
@Override
public View getChildAt(int index) {
return super.getChildAt(index);
}
/**
* Returns the number of items in the adapter bound to the parent RecyclerView.
* @return The number of items in the bound adapter
*/
@Override
public int getItemCount() {
return super.getItemCount();
}
/**
* Returns the item View which has or contains focus.
*
* @return A direct child of RecyclerView which has focus or contains the focused child.
*/
@Override
public View getFocusedChild() {
return super.getFocusedChild();
}
/**
* Returns the adapter position of the item represented by the given View. This does not
* contain any adapter changes that might have happened after the last layout.
*
* @param view The view to query
* @return The adapter position of the item which is rendered by this View.
*/
@Override
public int getPosition(View view) {
return super.getPosition(view);
}
/**
* 获取列数
* @return
*/
@Override
public int getSpanCount() {
return super.getSpanCount();
}
/**
* Called when searching for a focusable view in the given direction has failed for the current content of the RecyclerView.
* This is the LayoutManager's opportunity to populate views in the given direction to fulfill the request if it can.
* The LayoutManager should attach and return the view to be focused. The default implementation returns null.
* 防止当recyclerview上下滚动的时候焦点乱跳
* @param focused
* @param focusDirection
* @param recycler
* @param state
* @return
*/
@Override
public View onFocusSearchFailed(View focused, int focusDirection, RecyclerView.Recycler recycler, RecyclerView.State state) {
// Need to be called in order to layout new row/column
View nextFocus = super.onFocusSearchFailed(focused, focusDirection, recycler, state);
if (nextFocus == null) {
return null;
}
/**
* 获取当前焦点的位置
*/
int fromPos = getPosition(focused);
/**
* 获取我们希望的下一个焦点的位置
*/
int nextPos = getNextViewPos(fromPos, focusDirection);
return findViewByPosition(nextPos);
}
/**
* Manually detect next view to focus.
*
* @param fromPos from what position start to seek.
* @param direction in what direction start to seek. Your regular {@code View.FOCUS_*}.
* @return adapter position of next view to focus. May be equal to {@code fromPos}.
*/
protected int getNextViewPos(int fromPos, int direction) {
int offset = calcOffsetToNextView(direction);
if (hitBorder(fromPos, offset)) {
return fromPos;
}
return fromPos + offset;
}
/**
* Calculates position offset.
*
* @param direction regular {@code View.FOCUS_*}.
* @return position offset according to {@code direction}.
*/
protected int calcOffsetToNextView(int direction) {
int spanCount = getSpanCount();
int orientation = getOrientation();
if (orientation == VERTICAL) {
switch (direction) {
case View.FOCUS_DOWN:
return spanCount;
case View.FOCUS_UP:
return -spanCount;
case View.FOCUS_RIGHT:
return 1;
case View.FOCUS_LEFT:
return -1;
}
} else if (orientation == HORIZONTAL) {
switch (direction) {
case View.FOCUS_DOWN:
return 1;
case View.FOCUS_UP:
return -1;
case View.FOCUS_RIGHT:
return spanCount;
case View.FOCUS_LEFT:
return -spanCount;
}
}
return 0;
}
/**
* Checks if we hit borders.
*
* @param from from what position.
* @param offset offset to new position.
* @return {@code true} if we hit border.
*/
private boolean hitBorder(int from, int offset) {
int spanCount = getSpanCount();
if (Math.abs(offset) == 1) {
int spanIndex = from % spanCount;
int newSpanIndex = spanIndex + offset;
return newSpanIndex < 0 || newSpanIndex >= spanCount;
} else {
int newPos = from + offset;
return newPos < 0 && newPos >= spanCount;
}
}
}
分析：在我们从第五行往下按的时候，第六行的view是重新加载的，当新的一行的item还没有加载出来的时候，去找焦点是找不到的，找不到焦点就会调用mLayout.onFocusSearchFailed()方法，
The onFocusSearchFailed method is a method of LayoutManager, which returns null by default. We can override this method when customizing GridLayoutManager. Please see the code for specific processing steps. In the RecyclerView source code, onFocusSearchFailed is a member method of the internal abstract class LayoutManager, which returns null by default.
The above is the whole content of this article, I hope it will be helpful to everyone's learning, and I hope everyone will support Scripting Home.